1. Field of the Invention
The present invention relates to an image processing apparatus configured to correct image data.
2. Description of the Related Art
By using single-scale Retinex algorithm for synthesizing enhanced images in which smoothed brightness components, edges and the like are extracted and enhanced, characteristics such as line segments, edges and the like in the images have been prevented from becoming small due to compression of the dynamic range (cf., for example, Jpn. Pat. Appln. KOKAI Publication No. 2005-182232).
When the image data is corrected in a system of separating the luminance into illumination components and contrast components by backlight correction or the like, subjecting the illumination components to dynamic range compression and synthesizing again the illumination components with the contrast components to correct the dark portion brightly, it is necessary to obtain peripheral illumination components by referring to alignment of the pixels in a wide range and correct the image data with a substantially constant gain, in order to maintain the local contrast.
However, since the illumination components are generally formed by a Gauss filter, a filter of large kernel size needs to be formed in order to obtain the illumination components of the pixels in a wide range. In consideration of an adequate range for maintenance of the contrast, the process amount becomes enormous.
If detection of the illumination components is executed in a narrow range, the images with no contrast are obtained since edges are crushed by regarding the variation in the luminance at the edge such as an object boundary or the like as the variation in the illumination components. Consequently, the separation cannot be sufficiently executed and the contrast cannot be saved.
The conventional image processing apparatus has a problem that a filter of large kernel size is required to obtain the illumination components of the pixels in a wide range and the process amount becomes enormous.